Input control logic for a code reading system

ABSTRACT

D R A W I N G A SYSTEM FOR PROCESSING A COLOR BAR CODE READ OPTICALLY FROM A CODED MEDIUM IS DISCLOSED. THE SYSTEM INCLUDES LOGIC FOR DETERMINING THE BINARY CODE FROM COLOR SIGNALS AND STORAGE MEANS FOR TEMPORARILY STORING THE BINARY CODE. LOGIC IS ALSO PROVIDED WHICH ALLOWS THE READING OF A DOUBLE FIELD TAG AND WHICH CHECKS THE PARITY AND THE SIZE OF THE CAPTURED MESSAGE. FURTHER, LOGIC IS PROVIDED FOR TRANSMITTING THE CAPTURED MESSAGE TO A UTILIZATION DEVICE.

Feb. 20, 1973 Q c, G|LBERG ETAL 3,717,750

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OOOO OOOOO OOOOOOO 36 $5 wm .a x95 82 0 9m 228 dd 0 0: 3 59 A 05:53 55 1 05:58 Eom OOOOOOO OOOO A 50% T: 0 2.. o wxmw o Eom QDIESO v6 United States Patent 3,717,750 INPUT CONTROL LQGIC FOR A CODE READING SYSTEM Robert C. Gilberg, Dayton, James P. Donohue, Fairborn,

and Rarnesh S. Patel, Kettering, Ohio, assignors to The National Cash Register Company, Dayton, Ohio Filed Dec. 7, 1971, Ser. No. 205,543 Int. Cl. G06k 7/12 US. Cl. 235-6111 E Claims ABSTRACT OF THE DISCLOSURE A system for processing a color bar code read optically from a coded medium is disclosed. The system includes logic for determining the binary code from color signals and storage means for temporarily storing the binary code. Logic is also provided which allows the reading of a double field tag and which checks the parity and the size of the captured message. Further, logic is provided for transmitting the captured message to a utilization device.

This invention relates to code detecting apparatus and more particularly to apparatus for detecting the code manifested by a series of three or more colored bars placed contiguously along a given path.

In todays world of business, it has become necessary to automatically input information into a desired business machine. To effect this desire, a compact code is attached to a medium and scanned by appropriate reading apparatus. The medium may, for instance, be a retail price tag, a credit card, a bank ledger card, or any other desired item useful for containing information. The coded information may include the price and the article inventory number in case of a retail price tag, or an account number in the case of a credit card or bank ledger card.

One type of code utilizes a series of contiguous colored bars of three or more different colors where each bar has a bar of a different color on each side thereof. The transition from one color to another color in this code represents a binary bit, and the binary bits of all transitions represent the desired information. The binary bits may be grouped by fours so that each group represents one decimal number. A more complete description of this code is given in United States patent application Ser. No. 837,850, now Pat. No. 3,671,722 filed June 30, 1969, by John 13. Christie, and a reader for this code is described in United States patent application Ser. No. 837,514, now Pat. No. 3,637,993 filed June 30, 1969', by John B. Christie, Dzintars Abuls, and Wilfridus G. van Breukelen, both of which applications are assigned to the present assignee.

When a coded tag is being used, it is essential that the encoded information be accurately read. In this regard, the tag includes control information such as a size code and parity information which is read by reading apparatus. Thereafter, logic in the reading apparatus checks the data against the size code and parity information to insure that the data is accurate.

When reading the above code it is desirable to store it in groups of two four bit characters. However the number of desirable control information bits may not fit into the two four bit character scheme. Thus, it is necessary to provide the necessary input control logic to compensate for this.

. In accordance with one preferred embodiment of this invention, there is provided in a code reading system for reading a coded medium detecting means for providing a series of bits, one at a time, in response to the code, each successive M bits provided constituting a character of bits, bit counting means responsive the the occurrence of each bit of the series for providing a first signal after each character of bits occurs, and input buffer means responsive to the application thereto of the series of bits for storing the bits applied thereto until a character of bits is stored thereby. There is further provided position counting means for continually counting from one to L, index counting means responsive to said first signal for being incremented each time the first signal occurs, and comparing means for providing a second signal whenever the counts of the position counting means and the index counting means are equal. Finally, there is provided main storage means for storing a character of bits applied thereto in a position thereof defined by the count existing in the index counting means, at the time the character of bits is applied thereto, the character of bits applied to the main storage means being applied from the input buffer means upon command of the second signal.

A detailed description of one preferred embodiment of this invention is hereinafter given with reference being made to the following figures, in which:

FIG. 1A shows a single field color bar tag;

FIG. 1B shows a double field color bar tag;

FIG. 2A shows the general layout of a single field tag;

FIG. 2B shows the general layout of a double field tag;

FIG. 3 shows a specific layout of the color bars in a field of a color bar tag;

FIG. 4A and 4B show code detecting charts;

FIG. 5 shows a general block diagram of the reading apparatus for reading the color bar tags shown in FIGS. 1A and 1B;

FIG. 6 shows the four phase clock signals used in operating the logic circuits of the present invention;

FIGS. 7 through 10 show, respectively, a 1, 2, 3, and 4 gate used as the building block logic elements of the present invention;

FIG. 11 is a chart showing which gate of FIGS. 7 through 10 ian drive which other gate;

FIGS. 12 and 13 are examples of how logic circuits can be built for given logic equations;

FIGS. 14A through 14L show a detailed block diagram of the reading apparatus of FIG. 5; and

FIGS. 15A and 153 show the position of dummy bits placed in the memory during the reading of the color bar tag.

Referring now to FIG. 1A, there is shown a typical single field tag 10 which can be used in a retail store. Tag 10 includes data field 12 consisting of a plurality of colored bars placed contiguous to one another. The bars may be of three different colors, such as green, black, and white, and the background color of tag 10 may be white. In practice, the data field is printed by printing the green and black bars and leaving a space for the white bars. A printer for printing the tag 10 is described in United States patent application Ser. No. 51,073, filed June 30, 1970, by Donald E. Landis and entitled Color Bar Printer. Tag 10 also includes several series of human readable printing 14, which manifests the essential information contained in the data field 12. This is provided so that the customer knows the price and also so that the information can be entered manually in the event of an equipment breakdown.

FIG. 1B shows a typical double field tag 20, which includes two color bar coded data fields 22 and 24 separated by an area 25. Data field 22 may include inventory control information such as department number, class number, stock keeping unit (s.k.u.) number, size, color, and so forth. This information is printed as human readable printing 26 to the side of data field 22. Data field 24 may include the price information, which is manifested by human readable printing 28. Data field 24 and printing 28 can be detached from tag 20 along perforations 30 in the event of a price change, and a new data field and associated printing manifesting the new price can be afiixed to complete tag 20 with the proper price information, or the price may be inserted manually, if desired.

Data fields 12, 22, and 24 may be scanned with a penlike device which is described in detail in the above-noted Christie et a1. United States patent application and which provides a signal indicative of the color of the bar then being scanned. These color signals are processed by logic circuitry to obtain the desired information, which is then transmitted to a utilization device, such as the retail sales terminal described in United States patent application Ser. No. 71,971, now Pat. No. 3,686,367, filed Sept. 14, 1970, by James E. Zachar and Walter E. Srode, Jr., and entitled Retail Terminal, which is assigned to the present assignee.

Referring now to FIG. 2A, there is shown the general coded layout of data field 12 of single field tag 10. Data field 12 includes front and back control data portions 32 and 34 and data portion 36. Front control data portion 32 includes a single direction bit, a four bit size code, and a two bit tag identification code. Back control data portion 34 includes a single direction bit, a four bit size code, a two bit MODS parity code, and a four bit block check code (B.C.C.) parity code. Data portion 36 may contain from 2 through 28 even numbers only (four bit binary coded decimal B.C.D.) characters.

FIG. 2B shows the general coded layout of the data fields 22 and 24 of double field tag 20. Data field 22 contains front control data portion 38, data 1 portion 40, and back control data portion 42, and data field 24 contains front control data portion 44, data 2 portion 46, and back control data portion 4ft. Area 25 is between back control data portion 42 and front control data portion 44. Front control data portions 38 and 44 contain a single direction bit, a four-bit size code, and a two-bit identification code. Back control data portions 42 and 48 contain a single direction bit, a four-bit size code, a twobit MODS parity code, and a four-bit B.C.C. parity code. Data 1 portion 42 and data 2 portion 46 contain from 2 to 28 even numbers only) four-bit B.C.D. characters.

FIG. 3 shows an example of a data field 50, which includes a plurality of individual color bars 52a-52gg each contiguous with one another. Field 50 may be either field 12 or one of fields 22 or 24. Each of the bars 52 is labeled either W," G, or B to indicate whether they are a respective white, green, or black bar. On the left and right of data field 50 are larger white areas 54 and 56. which are part of the background of the tag. If field 50 is one of the fields of a double field tag, one of the areas 54 or 56 will be area 25 shown in FIGS. 18 or 2B. The colors of the bars 52a-52gg are so arranged that no bars of the same color are adjacent to each other.

In coded tags, such as those shown in FIG. 1 through 3, it is desirable that the coding be capable of being scanned in either direction; that is, from top to bottom, or from bottom to top, in the case of FIG. 1, and from right to left or from left to right in the case of FIGS. 2 and 3. To accomplish this in the code of FIG. 3, the leftmost bar 52a is green, and the rightmost bar 52gg is black. A forward direction scan is defined when data field 50 is scanned from green bar 52a to black bar 52gg (left to 4 right in FIG. 3), and a reverse direction scan is defined when data field 50 is scanned from black bar 52gg to green bar 52a (right to left in FIG. 3). Logic within the reader (to be hereinafter explained in detail) will look at the first binary bit detected and provide a signal indicative of the direction scanned.

Before a discussion of the coding layout of FIG. 3 in detail, it is necessary to understand the code itself. For this, reference is made to FIGS. 4A and 4B, where two code decipher charts are shown. The color bar code is a transition code; that is, the transition from one color to another color represents a binary digit (bit) of either 1 or 0. Specifically, as shown by FIG. 4A, transitions from white to green, green to black, and black to white represent 0 bits, and, as shown by FIG. 4B, transitions from white to black, black to green, and green to white represent 1 bits.

Referring again to FIG. 3, it is seen that the first transition in a forward direction scan is from white background area 54 to green bar 52a, and this represents a 0 bit. On the other hand, the first transition in a reverse direction scan is from white background area 56 to black bar 52gg, and this represents a 1 bit. Since the first bar 52:: will always be green and the last bar 52gg will always be black, the first bit detected represents the direction of the scan. It should be noted that the bit values determined in a reverse scan will be in opposite order and the complement of the bit values obtained while scanning in the forward direction. For instance, the last bit detected in a forward direction scan will be a 0 bit due to the black bar 52gg to white background area 56 transition, whereas this transition occurs first and represents a 1 bit for a reverse direction scan.

For brevity hereinafter with respect to FIG. 3, the coding format of data field 50 will be described as being scanned in the forward direction, it being understood that for a reverse direction scan oppositely ordered complementary bits are provided. Bars 52b52e form the front size code and are selected so that the transitions to those bars will give the complement of one more than the number of eight-bit characters in the data portion, with the most significant bit of the front size code being scanned first. It should be noted that each eight-bit character includes two four-bit B.C.D. digits. Thus, the number of four-bit B.C.D. characters will be (2N-2), where N is the size code number which is defined by the complement of the front size code.

The bars 52; and 52g form an identification code (I.D.) to indicate whether a single field tag, such as the tag 10, or a double field tag, such as the tag 20, is being scanned. If the transitions to these bars produce the binary code 0 0, a single field tag is being scanned; if the transitions to these bars produce the binary code 0-l (most significant digit first), the first data field of a double field tag is being scanned; and if the transitions to these bars produce the binary code l-l, the second data field of a double field tag is being scanned. For a reverse direction scan, these binary codes will be reversed and comple mented.

Next, the data contained in the data field is scanned by determining the transitions to bars 5211 through 52w. As previously mentioned, each four successive bars constitute a B.C.D. character, and there are (2N-2) B.C.D. characters of data, where N is the number in the size code, arranged most significant character first, with each B.C.D. character being arranged least significant bit first.

After the data of the data field 50 is detected, bars 52x52aa are scanned, and the transitions to these bars provide the four-bit B.C.C. parity code. The B.C.C. parity code is determined by adding the 1" bits in each significant position of each B.C.D. character, and dividing this sum by two, the remainder being the B.C.C. code. For example, for the four B.C.D. characters 0100,"

adding the 1 bits: dividing each sum by 2: quotient:

remainder (B.C.C.):

Thus, the B.C.C. Parity code is 1-0-0O.

After the B.C.C. parity code has been detected, a twobit MOD3 parity code is detected by finding the transition to bars 5212b and 5200. These two bits will insure that the last bar 52gg will be black in addition to affording a second parity check. The MOD3 parity code is determined by counting the total number of 1 bits and bits in the entire data field, excluding the MOD3 parity code, dividing each of these sums by 3, and adding a sufficient number of 1 bits as the MOD3 parity code to make the remainders equal. For example, if in a data field there are twenty 1 bits and twelve 0 bits, the MOD3 code is calculated as follows:

divide 0 total by 3: 20/3=6, remainder 2 divide 1 total by 3: 12/3=4, remainder 0 remainder difierence: 2

Thus, two 1 bits are needed to make the remainders equal, so the MOD3 parity code will be 1-1.

Following the MOD3 parity code is the back size code, which is determined by the transition to bars 52dd through 52gg. In the case of the back size code, the true values of the bits are scanned, least significant bit first. Thus, the back size code is in opposite order and complementary to the front size code. This results in the second through fifth bits of the code being the same regardless of whether the data field is scanned in a forward or a reverse direction. The final bit in the data field 50 will be the direction bit defined by the transition from bar 52gg to background area 56, and this will be the same as the original direction bit defined by the transition from background area 54 to'bar 52a.

Referring now to FIG. 5, a generalized block diagram of the Color Bar Reader 60 is shown. A color bar field 62 is scanned by an optical pen-shaped probe 64. Light rays indicative of the color then being scanned are transmitted through a fiber optic bundle 66 to Color Detector Circuit 68. Color Detector Circuit 68 provides three pulse shaped signals which indicate the color then being scanned. If a white color bar is scanned, the WHL signal is a logic 0 signal, and the GNL and BKL signals are logic 1 signals. Similarly, if a respective green or black color bar is being scanned, the respective GNL or BKL signals are logic 0, and the other two signals are logic 1 signals. A detailed description of the probe 64, the fiber optic bundle 66, and the Color Detector Circuit 68 is given in the above-mentioned Christie et al. United States patent application.

The three color signals WHL, GNL, and BKL are applied to Data Decoder Means 70, which provides a DATAIN signal, which is the binary coded signal of the code in data field 62. The DATAIN signal is applied to Input Buffer Means 72, and, after eight bits have been applied thereto, the RGIXCP signal becomes logic 1 and causes the eight bits in Input Buffer Means 72 to be transferred as the IBB8 signal to character position one of the Main Buffer Means 74.

Main Buffer Means 74 includes a 136-bit Main Buffer A76 and a second 136-bit Main Buffer B78, each of which has respective control circuits MBA Control Means 80 and MBB Control Means 82 associated therewith. For a single field tag, or the first scanned field of a double field tag, the information detected is stored in Main Buffer A76, and, for the second scanned field of a double field tag, the information detected is stored in Main Buffer B78. The term first scanned field is defined to be data field 22 in FIG. 2B for a forward direction scan and data field 24 for a reverse direction scan. The term second scanned field is defined to mean field 24 for a forward direction scan and field 22 for a reverse direction scan.

Upon command of the RGIXGP signal, an eight-bit character is shifted from Main Bufiier Means 74 through Output Buffer Control Logic 84 and Output Buffer Means 86 to Interface Means 88. Interface Means 88 Interfaces the Reader 60 with an appropriate Utilization Device 89, such as the Terminal Control Unit shown in the abovecited Zachar et al. United States patent application and further described in United States patent application Ser. No. 72,084, filed Sept. 14, 1970, by Ralph D. Haney et al. and entitled Digital Processor, which is assigned to the present assignee. Before Interface Means 88 transmits any data to Utilization Device 89, the data must be checked to insure its accuracy. For this, the remainder of Reader 60 is provided.

The WHL, GNL, and BKL signals from Color Detector Circuit 68 are also applied to a Beginning Of Field (BOP) Counter Means 90, and End Of Field ('EOF) Counter Means 92 and Transition Detector Means 94. BOF Counter Means 90 counts the time the WHL signal is logic 0 and compares this time to the time the next G'NL or BK-L signal is logic 0. If it turns out that the GNL or BKL signal time is less than one fourth the WH-L signal time, the BOP signal becomes a logic 1. This indicates that a transition from the white background color to the first bar has occurred. Similarly, 'EOF Counter Means 92 counts the time a BKL or a GNL signal is logic 0 and compares this time to the time the immediately subsequent WHL signal (if any) is logic 0. If the WHL signal is logic 0 four times as long as the previous GNL or BKL signal, the EOF signal becomes logic 1." This indicates that the last transition of the data field has occurred.

Every time a color transition occurs and a DATAIN bit is provided, Transition Detector Means 94 provides an LDNB signal and a TRANSTB7 signal, and these signals are applied to BC8 Counter Means 96. The LDNB signal is also applied to Input Buffer Means 72 to enable the DATAIN bit to be applied thereto. BC8 Counter Means 96 increments its count from one to eight each time the LDNB signal occurs and the count therein at any time equals the number of bits stored in Input Buffer Means 72.

In addition to BC8 Counter Means 96, four other counters are included in Reader 60. These are Register Position Counter Means 98, Index Register Counter Means 100, Limit Register Counter Means 102, and Gross Time Out (GTO) Counter Means 104. Register Position Counter Means 98 is a free-running counter which continually counts from one to seventeen. It is used to keep track of the information in Main Bufier Means 74. Index Register Counter Means 100 works in conjunction with Register Position Counter Means 98 to load and unload data into and out of Main Buffer Means 74. It is incremented by each BC8 pulse provided from BCS Counter Means 96. Limit Register Counter Means 102 is used in conjunction with Index Register Counter Means 100 to compare the length of the data, to add four dummy bits into Input Butter Means 72, and to detect the end of data. It is used in conjunction with Register Position Counter Means 98 to detect the end of message and initiate the parity check. The size code from Output Buifer Means 86 is applied to Limit Register Counter Means 102 and stored therein for future reference. GTO Counter Means 104 is a switchable counter which provides a PENUP signal either if probe 62 scans the same color for either one fourth of a second or one second, depending upon whether a color bar, or area 25, shown in FIGS. 1B and 2B, is being scanned. It is incremented by the RSTRPC signal provided from Register Position Counter Means 98 and reset by each TRA=NSTB7 pulse from Transition Detector Means 94, The PENUP signal is provided one fourth of a second after the last transition in case a bar is being scanned and after one second in case area 25 of a double field tag is being scanned. The switchability of GTO Counter Means 104 is controlled by the size code and the ID code in the first scanned data field.

Register Position Counter and Index Register Counter (RFC. and LRJC.) Compare Means 106 provides an eight-bit-long RGIXCP signal every time the count in Register Position Counter Means 98 equals the count in Index Register Counter Means 100. This signal allows the data transfer between Input Buffer Means 72 and Main BulTer Means 74 and between Main Buffer Means 74 and Output Buffer Means 86. Register Position Counter and Limit Register Counter (RPC & LRC) Compare Means 108 provides an RGLRCP pulse signal whenever the count in Register Position Counter Means 98 equals the count in Limit Register Counter Means 102. Limit Register Counter and Index Register Counter (LRC & IRC) Compare Means 110 provides an LRIXCP signal whenever the count in Limit Register Counter Means 102 equals the count in Index Register Position Counter Means 98.

After the entire data field has been scanned, it is necessary to provide an End of Data (EOD) signal. This signal is provided after two size code checks have been performed by Size Code Check Means 112. The first size code check is comparing the first size code detected with the second size code detected and is accomplished as follows. After the first eight bits are detected and stored in Input Buffer Means 72, they are transferred to both Main Buffer Means 7 4 and Output Buffer Means 86, causing the first detected size code to be stored in Output Buffer Means 86. After the last data bit is detected from the tag and the EOF signal becomes logic 1, the second detected size code is in Input Buffer Means 72. At this time, the size codes in both Input Buffer Means 72 and Output Buffer Means 86 are applied to Size Code Check Means 112 as the GED and IBBS signals and compared with one another. The second size code check is performed by also applying the OED signal to Limit Register Counter Means 102, so that the size code is also stored therein. It should be noted that at this time (after the EOF) signal) the count in Index Register Counter Means 100 will be one less than the total number of eight)bit characters detected, since the last detected character is still in Input Buffer Means 72 and the count in Limit Register Counter 102 reflects the size code number, which is two less than the total number of eight-bit characters scanned. If the front and back size codes properly compare in Size Code Check Means 112, the count in Limit Register Counter Means 102 is increased by two, and the count in Index Register Counter Means 100 is increased by one. If all bits of the code have been detected, this should make the count in Index Register Counter Means 100 equal the count in Limit Register Counter Means 102, thereby causing the LRIXCP signal to become a logic 1. When the RGIXCP signal becomes logic 1, the BOD signal will become logic 1, indicating that the two size code checks have been successfully completed.

If one or both of the two size code checks are unsuccessful, it is still desirable for the BOD signal to become logic 1." This will occur after the GTO counter 104 provides the logic 1 PENUP signal, due to probe 64 remaining on white background area 56 in FIG. 3.

After the size code has been checked, the B.C.C. and MOD3 parity of the captured data is checked. The EOD signal is applied to Parity Loop Control Logic 114 and causes the SCPYOT signal and the PTYSEQ signal to be set to logic I. The SCPYOT signal is applied to Character Pulse Generator Means 116 and set the CHPLOT signal for one character time (eight bit times). This causes Index Register Counter Means to be set to a count of one, and, when Register Position Counter Means 98 has a count of one, the RGIXCP signal becomes logic 1 for one charatcer time. This clears Index Register Counter Means 100 and causes the first eight control bits stored in the first position of Main Butter Means 74 to be shifted into Output Buffer Means 86. The size code in these eight bits is then shifted to Limit Register Counter Means 102, and two is added to the count in Limit Register Counter Means 100, so that the count therein corresponds to the number of characters in Main Buffer Means 74.

At this time, the PYCKFF signal is set to logic 1," and it resets the SCPYOT signal and causes the CHPLOT signal from Character Pulse Generator Means 116 to be set for one character time. This, in turn, causes a count of one to be placed in Index Register Counter Means 100, and the RGIXCP signal becomes logic 1 when the count in Register Position Counter Means 98 becomes one. Now the RGIXCP signal is held at logic 1 until the count in Register Position Counter Means 98 matches the count in Limit Register Counter Means 108; that is, until the RGLRCP signal becomes logic 1. During this time, all of the bits in Main Buffer Means 74 are shifted through Parity Check Logic Means 118, and the B.C.C. and MOD3 parity of the data stored in Main Buffer Means 74 is checked. If the parity check is successful, then the PYCKFF and PTYSEQ signals are reset to logic 0.

At this time, the data has been completely checked and is ready to be transmitted to Utilization Device 89. After the PTYSEQ signal is reset, the SCDTOT signal from Data Loop Logic Means 120 is set. This signal sets the CHPLOT signal to logic 1 for one character time and causes a count of one to be placed in Index Register Counter Means 100. When the next RGIXCP signal occurs, the first character in Main Buffer Means 74 is shifted into Output Buffer Means 86, and the size code portion thereof is placed in Limit Register Counter Means 102. Then the DATAOT signal becomes logic 1," and the data transfer commences.

If the tag had been scanned in the forward direction, the CHPLOT signal is set for two character times, causing a count of two to be placed in Index Register Counter Means 100. When the RGIXCP signal becomes logic 1, the first eight-bit character of true data is shifted from position two in Main Buffer Means 74 to Output Buffer Means 86. Upon command of Utilization Device 89, the data in Output Buffer Means 86 is then right shifted and transmitted through Interface Means 88 to Utilization Device 89. During this time, Index Register Counter Means 100 is incremented by one, and, upon the next logic 1 RGIXCP signal, the next eight bits of data are transferred to Output Buffer Means 86'. This sequence continues until the count in Index Register Counter Means 100 equals the count in Limit Register Counter Means 102. Then, when the last data character is sent to Output Buffer Means 86', the LRIXCP signal becomes logic 1 and indicates that no more data is to be sent.

If the tag had been scanned in the reverse direction, the data stored in Main Buffer Means 74 would have been stored in opposite order and complementary to the data which is to be sent to Utilization Device 89. In this case, the SCDTOT signal causes the size code to additionally be loaded into Down Counter 122. Whenever the count in Down Counter I122 is fifteen or less, a one-character-long DWINSP signal is produced, and this signal is applied through CHPLOT control gate 124 to provide a logic 1 FDBKDOT signal, since the REVDAT signal is true for a reverse scan. The FDBKDOT logic 1 signal sets the CHPLOT signal, which remains logic 

